without having an idea of budget, and you've cast the net fairly wide, and depending on what era you like, I will add my comments to the "get an SOHC4" post above.  Ive got a CB400F and I really like it.  not everyones cup of tea, but a very well regarded thing in its day.  Handles OK (again, for its day) but the big difference between an old bike and a new bike is brakes, followed by tyres, followed by ability to go round a turn.  I think its called "handling" and the Japs didnt really get that till the mid-late 80's.   I think I could use the 400F as an "only" bike and not feel too short changed.  Bits are available (ebay and David Silver are your friends)   Its a nice looking thing, too.  If you are in Chch you are welcome to take it for a spin (its not insured though).
CB750's (SOHC and DOHC) are BIG:  215kg dry if I remember, and 67hp when new.  CB550s are cool as well but a 400F is nearly as quick and handles as well or better.
People want crazy money for them though, a completely mint 400F sold on tardme last year for $4500 (I should have bought it...)
You might have a think about some 80's stuff: (like the VF750F I have in my garage for cheap....) something like a GPz750, Gpz900, or something like that. 
Suzuki GSX750 or 1100 maybe a Katana (dreadfully uncomfortable but soooo cool).   The key to something this old is condition and maintenance history.
				
			 
			
		 
			
				
			
			
				I thought elections were decided by angry posts on social media.  - F5 Dave
			
			
		 
	
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